[amsat-bb] Re: S-band on Eagle
sco at sco-inc.com
Thu Sep 7 20:53:03 PDT 2006
Guess what, my Direct TV sat dish will not work in a heavy rain storm
here. Microwaves don't get through the rain or my vast trees when the
leaves are out. V band does, U band too. But S and C bands won't. I
wonder if C band signals will be blocked by the wood in the trees
even when the leaves are down?
If my highly pointed S band dish is on my roof and tracking the sat
in the sky and my nearest neighbor is more than 150 feet from my
antenna how can my neighbor's telephone, with very limited range
knock out the signal from Eagle, when I am using my SSB preamp?
I guess I just don't get the science to this. The FCC seems to think
that BPL signals going down my power lines are not a problem, so why
is one telephone or computer network from my neighbor going to stop
me from working P3E or Eagle (if it had S Band)?
And guess what no 2.4 ghz devices will get any closer to my antenna 5
or 10 or even 20 years from now unless i move. So that argument does
not hold water for me.
At 09:40 PM 9/7/2006, you wrote:
>Ladies and gentlemen:
>I have been reading the comments regarding the Eagle S-band downlink
>decision. I herewith respond to some.
>All along, the Eagle project has put a premium on hard science, rigorous
>peer review, and dispassionate analysis.
>All along we knew there might or would be some changes to what we've
>With several other issues on the move or decided, we took a few days in
>late June to hammer out, based on science, the transponder situation.
>We did multiple, independent link analyses, and all came to the same
>conclusion. We validated interference predictions with measurements
>that have been taken. The conclusion is that S-band is marginally
>useful as a downlink today (unusable in many locations), and by the time
>Eagle is launched, and through it's lifetime, will be unusable.
>Personally, I do not like this decision. I have S-band equipment that I
>was looking forward to using.
>Personally, I can live with this decision, and defend it to myself, let
>alone anyone else, because I am convinced that it is technically sound.
>As one of you commented this evening, AO-40 wasn't exactly a rock
>crusher on S-band. It worked, and adequately, at least on CW, but was
>not great. As I reflect on my personal AO-40 experiences, I now
>understand that there are 2 reasons for my disappointment. Local noise
>was one, and transponder distortion was another -- the latter will be
>corrected by SDX. S-band on AO-40, by necessity not choice, got many of
>us out of our comfort zones and convinced us that microwaves really
>aren't that hard. Let's enter the realm of S up and C down with that
>REMEMBER THAT AMSAT IS DEVELOPING THE GROUND STATION ALONG WITH THE
>You will not be left on your own to develop ground equipment. You will
>not be asked to mortgage your house; affordability by the masses is a
>key component of the design for the entire system.
>Comparison with AO-51 is an "apples and oranges" thing. The path losses
>are much different. FM is very unlike CW/SSB or wideband digital
>modes. Remember that a goal of the Eagle system is that everything is
>on all the time. No more matrix switches, no more schedules. We need
>up and downlinks to be useful throughout the entire orbit.
>Why did we "regress" to U/V? For one reason, many of you asked for it,
>and some of us worked hard to somehow incorporate that capability in
>response to member's desires. The foot in the door was the utility of a
>V-band beacon in case everything else goes sour. The forcing function
>was as follows. A goal of Eagle has always been some kind of hand-held
>or jump bag portable ground station capability for entry into the
>emergency area while the tsunami waters are receeding and the hurricane
>winds are down to gale force. Many of us thought we could take
>advantage of the gain in small antennas to do this on the microwaves.
>Rigorous link analysis led us to the conclusion that the best place to
>do this is U/V -- both from a RF/DC power perspective, and from a link
>standpoint. This leads to the digital and "traditiona"l transponder
>package for U/V, implemented in SDX.
>Why not also include a (switchable) S-band downlink in parallel with the
>V-band? Remember, no switches. Also, we run into an antenna space
>problem. We've already increased the size of the spacecraft from where
>we started, and for many reasons, do NOT want to build something as
>large as AO-40.
>A couple of you have commented this evening that perusing EaglePedia has
>not revealed the details of the decisions. That is because, while Bob
>McGwier (N4HY) and I have been working on the report of the meeting, it
>is not public. We've been working hard on it since June, in and around
>other AMSAT, ham radio, and life events. Shortly after I push send on
>this message, I'll begin my final look at that document prior to public
>Before I go spend time with the spousal unit TONIGHT, I will finish it
>and publish it. I will send an announcement on the amsat-bb that it is
>public. To read the report, go to the EaglePedia main page, and select
>project index. From there, select Team and Meetings, and there will be
>several options, not all public. The San Diego meeting minutes will be
>obvious and public.
>Several of you have commented, "If S-band is unusable, why is it flying
>on P3E?" Fair question, but I can't answer for AMSAT-DL. I DO know
>that the P3E system design is considerably older and farther along than
>Eagle. Eagle design decisions were made based on the best information
>in June of 2006.
>Aspects of this discussion have been worthy of /dev/null. More aspects
>of this discussion have raised valid points and reasonable questions,
>deserving of response, which is why I've been composing this note for
>the last four hours or so.
>A few have raised the old allegation of the builders doing what they
>want, without regard to users needs. This is not true. While the
>desire to advance the state of the art (part of amateur radio's
>justification for existence and allocation of valuable spectrum) leads
>to enthusiasm and study of potentially useful new techniques, this
>desire had no impact on our analysis-based decisions. We started with
>requirements and services, and explored what would deliver.
>I thank all of you for your interest and support. Your Eagle team is
>working hard to develop a system that will serve our needs, as well as
>advance the state of the art. As promised, we are making decisions
>based on sound, peer-reviewed science, not anybody's opinions or desires.
>Please read the report, study the spreadsheets, download the excel file
>and play with it. If you can, make your own measurements and put those
>numbers into the spreadsheet. I think you'll understand how these
>decisions were reached.
>After contemplating the report, send me your questions. I'll either
>respond or forward to he who can best respond. Another fundamental
>tenet of the Eagle project is openness, so you have a right to a
>response to a rational question. Please recognize that we're volunteers
>too, and subject to the realities of day jobs, families, and a real
>life. Response may not be instantaneous.
>Thanks again and very 73,
>James A. Sanford, PE
>Eagle Project Manager
>wb4gcs at amsat.org
>Sent via AMSAT-BB at amsat.org. Opinions expressed are those of the author.
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